1. Field of the Invention.
This invention relates to pressure-to-electrical switches and more particularly to the use of a single flexible diaphragm subjected to single source of varying control pressure to control by mechanical movement of the diaphragm, the operation of a plurality of electrical switches, each being actuated at its own adjustable pressure level.
2. Description of the Prior Art.
It is known to control electrical switches using pressure responsive diaphragms. Such teachings are found in the following U.S. patents: U.S. Pat. Nos. 4,273,976 granted to Wolford et al on June 16, 1981; 4,255,630 granted to Hire et al on March 10, 1981; 4,343,974 granted to Hire et al on Aug. 10, 1982; 2,766,349 granted to Hamburg on Oct. 9, 1956; 3,277,441 granted to Gutjahr on Oct. 4, 1966; 3,657,501 granted to Hoyt on April 18, 1972; and 4,591,677 granted to Hirota et al on May 27, 1986.
The patent to Wolford et al shows a single piece of rubber forming a diaphragm with a first set of magnets placed on the diaphragm in spaced relation with respect to each other. Different parts of the diaphragm are biased to resist diaphragm pressure by different amounts. Because of this differential, first magnets on the diaphragm act on aligned second magnets initially spaced from the diaphragm to activate separate switches under the force of different diaphragm pressures.
The patents to Hire et al each show one movable diaphragm portion simultaneously moving three or four electrical contacts.
In the patent to Hamburg, control pressure on a single portion of a single diaphragm controls first and second switches at two different pressure levels by using biasing springs of different strengths.
The patent to Gutjahr shows a single diaphragm portion operating a stepping switch whereby a number of switches in concentric relation to the movable diaphragm portion are opened serially upon application of an ever-increasing pressure against the diaphragm.
In the Hoyt patent, one area of a single diaphragm operates several pistons, the pistons successively operating as a series of stepping switches.
Lastly, the patent to Hirota et al shows a three-function switch including a single diaphragm having a single movable portion controlling the three switches by diaphragm movement along the single axes.
Other U.S. patents which are not believed to be particularly pertinent include U.S. Pat. Nos. 2,551,526 granted to Campbell on May 1, 1951; 2,421,149 granted to Segerstad on May 27, 1947; 3,952,284 granted to Martin on April 20, 1976; and 2,191,965 granted to McGrath on Feb. 27, 1940.
In the Campbell patent, a number of "limp" diaphragms are shown to lie in a single plane. A first side of each such limp diaphragm is fed the pressure developing along a different point in an airplane wing. The other side of each diaphragm is subjected to a constantly varying (sine wave) pressure. At the point the varying pressure on the second side of the diaphragm overcomes a particular predetermined pressure to be measured, a recording stylus relating to that diaphragm is lifted from a rotating chart.
The patent to Segerstad shows a single diaphragm situated to be controlled by a differential in pressure from two separate sources.
The Martin patent shows a single hydraulic tube open to three separate cylinders to move pistons in these cylinders to operate against three adjustable springs to that each piston can be sent to initially close its own electrical contact at its own preselected pressure.
Finally, the McGrath patent shows three pressure-to-electric switches controlled by three separate bellows fed by three different capillary tubes to operate separately under three separate conditions.
Means for serially putting electrically resistive heating elements "on the line" one after the other responsive to increases in pneumatic pressure is shown in the data sheets for Robertshaw Controls Company Model R450 Pneumatic Step Controller; and Johnson Controls G-180 Pneumatic Step Controller.
The Robertshaw controller includes a series of switches set to operate at different pressures. Each switch is operated by its own single diaphragm. This Robertshaw Model R450 has been in commerce for a considerable period of time before May 31, 1988.
The Johnsons Control Model G-180 Pneumatic Step Controller includes six, eight or twelve snap-acting single pole, double throw switches activated by individually adjustable "on" and "off" cams which are mounted on a common shaft which is rotated by a pneumatic actuator. This model has been in commerce since before Jan. 1, 1978.
The inventor and those in privity with him are aware of no prior art more pertinent than that discussed above. Neither he nor they are aware of any prior art which anticipates the present invention or the claims set out herein.
What was missing before the present invention was a pneumatic-to-electrical switch assembly in which a single diaphragm, which is subjected to a single source of varying control pressure on its first side, is provided with multiple pressure responsive switch control portions, each pressure responsive switch control portion being operative to activate its own electrical switch at a pressure on the diaphragm first side as determined by the setting of an easily adjustable, predetermined bias exerted on its switch control portion on a second side of the diaphragm.